Do not test the electrical system as your second non-mechanic recommended! You will ruin the alternator if you do!
Apparently you have never ever been told that all icons, rings, bells, etc on the dashboard are covered in the car manual. Rules of car ownership include to read the car manual. Every time any car operator turns the key on a car from OFF to ACC to RUN to START, there is a sequence of steps. With the car engine not running, thusly the alternator not working, the car battery icon is ON. Why? Find out. Ford Taurus. Proper names and must be capitalized the same as the first word of EACH sentence. Why are you not writing correctly? Owning or operating a car is more than a key and fuel. Too bad our culture cannot get our children educated enough as to cars and the language. This is a classic example. Asking here is not going to repair this car. Find a mechanic. Find an English grammar book. You need both.
An alternator drive belt is often a likely candidate and a new one is much less costly then say a new or rebuilt alternator. About your alternator--it tested good so why replace it. Check that no engine compartment fluids are causing alternator drive belt slippage.
The only advice I can give you is quit going to Walmart and expecting to find real mechanics where they only end up with high school drop outs that are barely qualified to mount tires and change your oil!
hears the thing even if that battery was taken out when the car was running it would stay running if the battery went dead while driving then the alternator is bad
battery light came on and I drove it till the battery died. took it to Walmart charged the battery and the battery charge held and my alternator output looked fine. battery light stayed off until I got home and came back. battery light comes and stays on and car stays in high idol until I hit the gas and force it to low idol. battery light then goes off and a high pitched noise comes on.
car is a ford 1999 taurus, 155,000 mi, tranny fluid checks out fine oil just changed.
any ideas?
